Control of exhaust energy in internal combustion engines

ABSTRACT

Methods of improving SCR performance in heavy duty vehicles may use multiple interdependent control techniques to increase engine exhaust temperatures in a fuel efficient manner. One method combines cylinder deactivation and mechanical loading of an engine by an electrical generator used to input energy into an exhaust stream to manipulate the exhaust temperature through the combined effect of modified air-to-fuel ratio and supplemental energy input. In particular, cylinder deactivation may be used to modify the engine air flowrate and the electric generator may be used to apply mechanical load on the engine to manipulate the engine fuel flow rate to control the engine air-to-fuel ratio and thereby increase exhaust temperatures. The exhaust temperatures may be further increased by using the electrical generator to add the energy generated as input energy to the exhaust stream.

BACKGROUND Technical Field

The present disclosure relates generally to control of exhaust energy ininternal combustion engines, and more particularly to fuel efficientcontrol of exhaust energy in internal combustion engines.

Description of the Related Art

Regulated emissions from today's heavy-duty engines demand very lowlevels of tailpipe emissions, and standards are expected to be furtherreduced in the near future. To reduce engine out exhaust emissions,current technologies rely on aggressive engine control strategies andexhaust after-treatment catalyst systems (catalyst systems used to treatengine exhaust are referred to herein as exhaust after-treatmentsystems, emissions after-treatment systems, or EAS). The EAS for atypical heavy-duty diesel or other lean-burning engine may include adiesel oxidation catalyst (DOC) to oxidize unburned fuel and carbonmonoxide, a diesel particulate filter (DPF) for control of particulatematter (PM), selective catalytic reduction (SCR) systems for reductionof oxides of nitrogen (NOX), and/or an ammonia oxidation catalyst(AMOX). Performance of EAS systems is dependent upon exhaust gastemperature and other parameters.

Additionally, SCR processes often use secondary fluid injection byinjecting a fluid referred to as DEF (diesel emission fluid), which actsas a NOX reductant over the SCR catalyst. DEF is an aqueous solutionthat evaporates and decomposes to chemically release and make availableammonia for reaction in an SCR system. A lower temperature threshold forefficient SCR operation exists at a lower temperature limit for DEFinjection, which is about 190° C. FIG. 1 shows a NOX conversionefficiency curve for a diesel SCR system, assuming that sufficientammonia is present. FIG. 1 also shows a range of operation over whichDEF injection is not feasible. In this range of operation, actual SCRefficiency is much lower than shown on the curve because sufficientammonia is not present.

Heavy-duty engines can be operated under a wide range of loadconditions, including highway driving, urban driving, and extendedidling. Proposed regulations include a new emissions test cycle referredto as the Low Load Cycle (LLC), which may be promulgated by one or moreof various governmental regulatory or standards-setting bodies, such asthe California Air Resources Board, and which includes lower engine loadpoints than current regulatory load cycles. The range of exhausttemperatures for current regulatory load cycles and in-use operation istypically high enough for suitable SCR catalyst operation, asillustrated in FIG. 2. Lower load operation, such as urban driving,however, can include extended idling and other motoring events thatresult in exhaust temperatures too low for suitable SCR catalystoperation. The proposed LLC includes heavy weighting on such idling andother motoring events, resulting in low exhaust temperatures. MeasuredSCR inlet exhaust temperature for a current production engine runningthe proposed LLC is shown in FIG. 3.

The proposed LLC is expected to require very high, such as greater than90%, SCR conversion efficiency to meet regulated emissions levels.However, as seen in FIG. 3, current production engines produce exhaustgas temperatures over much of the proposed LLC that are too low forsuitable DEF injection, and that are too low for suitable SCR catalystoperation even if DEF injection is feasible, as shown in FIG. 4.

BRIEF SUMMARY

A method may be summarized as comprising: warm idling an internalcombustion engine, thereby producing exhaust; reducing a volumetric flowrate of air through the engine; increasing a mechanical load to theengine, thereby increasing an amount of fuel demanded by the engine; andinputting energy from a source of electrical energy into the exhaust.Increasing a mechanical load to the engine may include using the runningengine to drive an electric generator. The method may further comprisecharging a battery with electric energy generated by the electricgenerator. The electric generator may be the source of electric energy.Inputting energy into the exhaust may include using an electricallyheated catalyst system.

Reducing the volumetric flow rate of air through the engine may includereducing the volumetric flow rate of air through the engine by half.Reducing the volumetric flow rate of air through the engine may includedeactivating one or more cylinders of the engine. Reducing thevolumetric flow rate of air through the engine may include recirculatingthe exhaust through the engine. Reducing the volumetric flow rate of airthrough the engine may include reducing an idle speed of the engine.Reducing a volumetric flow rate of air through the engine may beperformed simultaneously or concurrently with increasing a mechanicalload to the engine and inputting energy into the exhaust.

A method may be summarized as comprising, simultaneously: idling aninternal combustion engine with at least one cylinder of the enginefiring and at least one cylinder of the engine deactivated, therebyproducing exhaust; using the idling engine to drive an electricgenerator; and inputting electrical energy generated by the electricgenerator into the exhaust. Idling the internal combustion engine withat least one cylinder of the engine deactivated may reduce a volumetricflow rate of air through the engine relative to idling the engine withall cylinders of the engine firing; using the idling engine to drive anelectric generator may apply a mechanical load to the engine andincrease an amount of fuel demanded by the engine relative to idling theengine without using the idling engine to drive an electric generator;reducing the volumetric flow rate of air through the engine andincreasing the amount of fuel demanded by the engine may reduce anair-to-fuel ratio within the engine and increase a temperature of theexhaust; and inputting electrical energy generated by the electricgenerator into the exhaust may increase the temperature of the exhaust.

A heavy duty vehicle may be summarized as comprising: an internalcombustion engine; an exhaust after-treatment system; and a controlsystem; wherein the control system, in operation, controls the vehicle,the internal combustion engine, and the exhaust after-treatment systemto simultaneously: idle or warm idle the internal combustion engine withat least one cylinder of the engine firing and at least one cylinder ofthe engine deactivated; use the internal combustion engine to drive anelectric generator; and input electrical energy generated by theelectric generator into exhaust produced by the internal combustionengine. The internal combustion engine may be a diesel engine. Theexhaust after-treatment system may include a diesel oxidation catalyst,a diesel particulate filter, a selective catalytic reduction system,and/or ammonia oxidation catalyst system.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 illustrates typical SCR conversion efficiency as a function ofexhaust temperature.

FIG. 2 illustrates a range of exhaust temperature operation for currentproduction engines on current regulatory load cycles and in-useoperation.

FIG. 3 illustrates exhaust gas temperatures for current productionengines over a proposed Low Load Cycle.

FIG. 4 illustrates ranges of exhaust temperatures for current productionengines on current regulatory load cycles and the proposed Low LoadCycle.

FIG. 5 illustrates exhaust gas temperatures as a function of engineair-to-fuel ratio for a six cylinder engine under baseline (sixcylinders firing) and cylinder deactivation (three cylinders firing)operation.

FIG. 6A provides a schematic diagram of a system including an engine andan EAS where a baseline energy equation applies.

FIG. 6B provides a schematic diagram of a system including an engine andan EAS where a modified version of the baseline energy equation applies.

FIG. 6C provides a schematic diagram of another system including anengine and an EAS where another modified version of the baseline energyequation applies.

FIG. 6D provides a schematic diagram of another system including anengine and an EAS where another modified version of the baseline energyequation applies.

FIG. 7 illustrated a vehicle including an internal combustion engine,and exhaust after-treatment system, an electrical generator, and acontrol system configured to control such components to perform themethods described herein.

DETAILED DESCRIPTION

In the following description, certain specific details are set forth inorder to provide a thorough understanding of various disclosedembodiments. However, one skilled in the relevant art will recognizethat embodiments may be practiced without one or more of these specificdetails, or with other methods, components, materials, etc. In otherinstances, well-known structures associated with the technology have notbeen shown or described in detail to avoid unnecessarily obscuringdescriptions of the embodiments.

Reference throughout this specification to “one embodiment” or “anembodiment” means that a particular feature, structure or characteristicdescribed in connection with the embodiment is included in at least oneembodiment. Thus, the appearances of the phrases “in one embodiment” or“in an embodiment” in various places throughout this specification arenot necessarily all referring to the same embodiment. Furthermore, theparticular features, structures, or characteristics may be combined inany suitable manner in one or more embodiments. Also, as used in thisspecification and the appended claims, the singular forms “a,” “an,” and“the” include plural referents unless the context clearly dictatesotherwise. It should also be noted that the term “or” is generallyemployed in its sense including “and/or” unless the context clearlydictates otherwise.

The use of ordinals such as first, second and third does not necessarilyimply a ranked sense of order, but rather may only distinguish betweenmultiple instances of an act or structure.

Terms of geometric alignment may be used herein. Any components of theembodiments that are illustrated, described, or claimed herein as beingaligned, arranged in the same direction, parallel, or having othersimilar geometric relationships with respect to one another have suchrelationships in the illustrated, described, or claimed embodiments. Inalternative embodiments, however, such components can have any of theother similar geometric properties described herein indicating alignmentwith respect to one another. Any components of the embodiments that areillustrated, described, or claimed herein as being not aligned, arrangedin different directions, not parallel, perpendicular, transverse, orhaving other similar geometric relationships with respect to oneanother, have such relationships in the illustrated, described, orclaimed embodiments. In alternative embodiments, however, suchcomponents can have any of the other similar geometric propertiesdescribed herein indicating non-alignment with respect to one another.

Various examples of suitable dimensions of components and othernumerical values may be provided herein. In the illustrated, described,and claimed embodiments, such dimensions are accurate to within standardmanufacturing tolerances unless stated otherwise. Such dimensions areexamples, however, and can be modified to produce variations of thecomponents and systems described herein. In various alternativeembodiments, such dimensions and any other specific numerical valuesprovided herein can be approximations wherein the actual numericalvalues can vary by up to 1, 2, 5, 10, 15 or more percent from thestated, approximate dimensions or other numerical values.

One approach to meeting regulated NOX emissions levels over the proposedLLC would be to introduce additional engine control systems and/orexhaust after-treatment devices, and to inject energy into the exhaustto increase its temperature to improve performance of the SCR systems.Such an approach may be similar to existing “cold start” solutions andmay incur a fuel penalty and increase overall fuel consumption, whichwould decrease engine efficiency and make it more difficult to meetcarbon emissions requirements. The present disclosure thereforedescribes approaches to meeting regulated NOX emissions levels over theproposed LLC by increasing a temperature of the exhaust, particularlyunder urban driving and idling conditions, while maintaining orsubstantially reducing the fuel penalty compared to baseline engineoperation.

In some embodiments, a method of improving SCR performance in a heavyduty vehicle including an internal combustion engine, such as a dieselengine, as well as a control system for controlling operation andperformance of the engine, includes operating the vehicle and itsengine, such as by driving the vehicle on highway and/or city streets,and/or idling the engine. As used herein, the term “idling” means thatthe engine is running but the vehicle is not moving, such that theengine powers parasitic or ancillary devices in the vehicle, such as airconditioning, radio, fans, etc., but is not used to propel the vehicle.As used herein, the term “warm idling” means that the engine has beenrunning for sufficient time such that its temperature is elevated aboveambient environmental temperatures and has stabilized or reached asubstantially steady state. Depending on the circumstances, thetemperature of a warm idling diesel engine or of a coolant therein maybe above 100 degrees Celsius or above 200 degrees Celsius. Operation ofthe vehicle and its internal combustion engine, whether the vehicle isdriving or the engine is idling or warm idling, produces exhaust gases.

In some embodiments, the method further includes controlling avolumetric flow rate of air through the engine, such as reducing thevolumetric flow rate of air through the engine, such as relative to abaseline volumetric flow rate of air through the engine. Reducing thevolumetric flow rate of air through the engine may comprise reducing thevolumetric flow rate of air by greater than 0%, 10%, 20%, 30%, 40%, 50%,60%, 70%, 80%, or 90%, and/or less than 10%, 20%, 30%, 40%, 50%, 60%,70%, 80%, 90%, or 100%, relative to the baseline volumetric flow rate ofair through the engine. Reducing the volumetric flow rate of air throughthe engine may comprise reducing the volumetric flow rate of air byhalf, or 50%, or between 45% and 55%, or between 40% and 60%, or between35% and 65%, or between 30% and 70% relative to the baseline volumetricflow rate of air through the engine.

In some embodiments, the volumetric flow rate of air through the engineis reduced by deactivating one or more cylinders of the engine, whichmay be referred to herein as cylinder deactivation or CDA. For example,if the engine has four total cylinders, the volumetric flow rate of airthrough the engine can be reduced by operating the engine with onecylinder firing and three cylinders deactivated, or with two cylindersfiring and two cylinders deactivated, or with three cylinders firing andone cylinder deactivated. As another example, if the engine has sixtotal cylinders, the volumetric flow rate of air through the engine canbe reduced by operating the engine with one cylinder firing and fivecylinders deactivated, or with two cylinders firing and four cylindersdeactivated, or with three cylinders firing and three cylindersdeactivated, or with four cylinders firing and two cylindersdeactivated, or with five cylinders firing and one cylinder deactivated.As another example, if the engine has eight total cylinders, thevolumetric flow rate of air through the engine can be reduced byoperating the engine with one cylinder firing and seven cylindersdeactivated, or with two cylinders firing and six cylinders deactivated,or with three cylinders firing and five cylinders deactivated, or withfour cylinders firing and four cylinders deactivated, or with fivecylinders firing and three cylinders deactivated, or with six cylindersfiring and two cylinders deactivated, or with seven cylinders firing andone cylinder deactivated. As other examples, the volumetric flow rate ofair through the engine can be reduced by operating the engine with onequarter, or one third, or one half, or two thirds, or three quarters ofits cylinders deactivated and the remaining cylinders firing.

In other embodiments, the volumetric flow rate of air through the engineis reduced by recirculating at least a portion of the exhaust gasesthrough the engine, which may be referred to as exhaust gasrecirculation or EGR. For example, recirculating at least a portion ofthe exhaust gases through the engine may comprise recirculating greaterthan 0%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, or 90%, and/or lessthan 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, or 100% of thevolumetric flow of the exhaust gases through the engine. In still otherembodiments, the volumetric flow rate of air through the engine isreduced by reducing a speed, such as in terms of revolutions per minuteor RPM, at which the engine and/or its firing cylinders run relative toa baseline speed of the engine and/or its firing cylinders, such aswhile idling (i.e., an “idle speed” of the engine). For example,reducing the speed at which the engine and its firing cylinders run maycomprise reducing the speed by greater than 0%, 10%, 20%, 30%, 40%, 50%,60%, 70%, 80%, or 90%, and/or less than 10%, 20%, 30%, 40%, 50%, 60%,70%, 80%, 90%, or 100% relative to a baseline speed such as a baselineidle speed and/or a speed when all cylinders of the engine are firing.While the volumetric flow rate of air through the engine may be reducedby any of the techniques described herein, it has been found thatcylinder deactivation is in many cases cleaner than other options interms of emissions and more efficient than other options in terms offuel use, and is therefore preferred in many embodiments.

In some embodiments, the method further includes increasing an amount offuel demanded by the engine and/or a flow rate of a fuel through theengine, such as relative to a baseline amount of fuel demanded by theengine and/or baseline flow rate of the fuel through the engine.Increasing the amount of fuel demanded by the engine or the flow rate ofthe fuel through the engine may comprise an increase of greater than 0%,10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, or 90%, and/or less than 10%,20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, or 100%, relative to thebaseline amount of fuel demanded and/or baseline flow rate of the fuelthrough the engine.

Increasing the fuel demand or the fuel flow rate through the engine maycomprise loading the engine by applying a mechanical load to the engine.In some embodiments, such a mechanical load may be an electricalgenerator, such as an alternator, a dynamo, or other electric generationdevice, which is driven by the engine to generate electric energy, suchthat operation of the electrical generator to generate electric energyapplies a mechanical load to the engine and thereby increases an amountof fuel demanded by the engine and/or increases a flow rate of the fuelthrough the engine. In some implementations, the vehicle can include abattery and the electric generator can charge the battery such that thebattery stores the electric energy generated by the electricalgenerator. Reducing the volumetric flow rate of air through the engineand increasing an amount of fuel demanded by the engine and a flow rateof fuel through the engine reduces an air-to-fuel ratio within theengine and can increase the temperature of the exhaust gases produced bythe engine. For example, combustion of more fuel in less air results inmore energy distributed across a smaller mass.

In some embodiments, the method further includes directly inputting orinjecting energy into the exhaust gases, thereby increasing theirtemperature. Inputting energy directly into the exhaust gases maycomprise inputting at least 0.5 kW, 1.0 kW, 1.5 kW, 2.0 kW, 3.0 kW, 4.0kW, 5.0 kW, 6.0 kW, 7.0 kW, 8.0 kW, 9.0 kW, 10.0 kW, 11.0 kW, 12.0 kW,13.0 kW, 14.0 kW, 15.0 kW, 16.0 kW, 17.0 kW, 18.0 kW, 19.0 kW, 20.0 kW,21.0 kW, 22.0 kW, 23.0 kW, 24.0 kW, 25.0 kW, 26.0 kW, 27.0 kW, 28.0 kW,29.0 kW, or 30.0 kW, and no more than 1.0 kW, 1.5 kW, 2.0 kW, 3.0 kW,4.0 kW, 5.0 kW, 6.0 kW, 7.0 kW, 8.0 kW, 9.0 kW, 10.0 kW, 11.0 kW, 12.0kW, 13.0 kW, 14.0 kW, 15.0 kW, 16.0 kW, 17.0 kW, 18.0 kW, 19.0 kW, 20.0kW, 21.0 kW, 22.0 kW, 23.0 kW, 24.0 kW, 25.0 kW, 26.0 kW, 27.0 kW, 28.0kW, 29.0 kW, 30.0 kW, or 31.0 kW into the exhaust gases. Inputtingenergy directly into the exhaust gases may comprise inputting 5.0 kW,between 4.5 kW and 5.5 kW, between 4.0 kW and 6.0 kW, between 3.5 kW and6.5 kW, or between 3.0 kW and 7.0 kW into the exhaust gases. In someembodiments, a fuel may be combusted, such as by a burner, within theexhaust gas stream to introduce thermal energy into the exhaust gasstream and thereby increase a temperature of the exhaust gas. In otherembodiments, a source of electric energy and/or an electrically heatedcatalyst (EHC) system are used to input the energy directly into theexhaust gases. Various suitable electrically heated catalyst systems areknown in the field and commercially available, such as under the brandname Continental Emitec, for such purposes.

Inputting energy such as thermal energy directly into the exhaust gasesin this manner increases the temperature of the exhaust gases. Further,inputting energy directly into the exhaust gases in this manner becomesincreasingly effective at raising the temperature of the exhaust gasesas the volumetric flow rate of air through the engine decreases, becausedecreasing the volumetric flow rate of air through the engine results insmaller volumetric and mass-based flow rates of exhaust gases generatedby the engine. Thus, under such conditions, a given amount of energyinput into the flow of exhaust gas or the exhaust gas stream results ina larger temperature increase in the exhaust gases than if thevolumetric flow rate of air through the engine had not been decreasedrelative to baseline levels.

In some embodiments, the electric generator described above that isdriven by and applies a load to the engine is the source of the energythat is input into the exhaust gas stream. For example, the electricgenerator can act as the source of electric energy by generatingelectric energy that is directly transmitted to the electrically heatedcatalyst system and input by the electrically heated catalyst systeminto the exhaust gas stream. As another example, the electric generatorcan act as the source of electric energy by generating electric energythat is transmitted to and stored in a battery, and then withdrawn fromthe battery and transmitted to the electrically heated catalyst systemand input by the electrically heated catalyst system into the exhaustgas stream.

In some implementations, an internal combustion engine idling underbaseline conditions can produce or generate at least 0.5 kW, 1.0 kW, 1.5kW, 2.0 kW, 3.0 kW, 4.0 kW, 5.0 kW, 6.0 kW, 7.0 kW, 8.0 kW, 9.0 kW, or10.0 kW, and no more than 1.0 kW, 1.5 kW, 2.0 kW, 3.0 kW, 4.0 kW, 5.0kW, 6.0 kW, 7.0 kW, 8.0 kW, 9.0 kW, 10.0 kW, or 11.0 kW of power. Suchpower can be used to drive parasitic components of the vehicle, such asair conditioning, radio, and/or fans, such as via an alternator. In someimplementations, the load of the electric generator demands and draws atleast 1.0 kW, 2.0 kW, 3.0 kW, 4.0 kW, 5.0 kW, 6.0 kW, 7.0 kW, 8.0 kW,9.0 kW, 10.0 kW, 11.0 kW, 12.0 kW, 13.0 kW, 14.0 kW, 15.0 kW, 16.0 kW,17.0 kW, 18.0 kW, 19.0 kW, 20.0 kW, 21.0 kW, 22.0 kW, 23.0 kW, 24.0 kW,25.0 kW, 26.0 kW, 27.0 kW, 28.0 kW, 29.0 kW, or 30.0 kW, and no morethan 2.0 kW, 3.0 kW, 4.0 kW, 5.0 kW, 6.0 kW, 7.0 kW, 8.0 kW, 9.0 kW,10.0 kW, 11.0 kW, 12.0 kW, 13.0 kW, 14.0 kW, 15.0 kW, 16.0 kW, 17.0 kW,18.0 kW, 19.0 kW, 20.0 kW, 21.0 kW, 22.0 kW, 23.0 kW, 24.0 kW, 25.0 kW,26.0 kW, 27.0 kW, 28.0 kW, 29.0 kW, 30.0 kW, or 31.0 kW of additionalpower from the internal combustion engine.

In some cases, a ratio of the amount of energy input into the exhaustgas stream, such as by an electrically heated catalyst system, to theamount of energy drawn from the internal combustion engine, such as byan electrical generator, can be 50%, between 45% and 55%, between 40%and 60%, between 35% and 65%, or between 30% and 70%. In some cases, aratio of an amount of energy input into the exhaust gas stream by anelectrically heated catalyst system to the amount of energy receivedfrom an electrical generator by the electrically heated catalyst system(e.g., the efficiency of the electrically heated catalyst system) isabout 90%, or between 85% and 95%, and a ratio of an amount of energygenerated by the electrical generator to the amount of energy drawn bythe electrical generator from the internal combustion engine (e.g., theefficiency of the electrical generator) is about 50%, or between 45% and55%.

Any or all of the actions or steps described herein may be performedsimultaneously or concurrently with one another, or within one second,two seconds, five seconds, ten seconds, thirty seconds, or sixty secondsof one another. Thus, the effects and advantages of each of the actionsor steps may interact with one another to compound the temperatureincreases resulting in the exhaust gas flow. The methods describedherein may also increase the energy content of an exhaust gas stream ata given operating speed over baseline conditions and operation.

Described herein are methods of improving SCR performance that includereducing air flow through an internal combustion engine, such as bycylinder deactivation. Such methods may also include mechanicallyloading the engine using an electric generator such as an alternator toincrease the power demanded of the engine, which while driving maintainsthe torque demand and while idling forces the engine to inject more fuelto maintain the engine's speed. For a fixed engine speed and a fixednumber of cylinders firing, the air flow will be maintained nearconstant, so the additional fuel will result in a change in engineair-to-fuel ratio. Under baseline operation, a diesel engine runs verylean, which results in cool exhaust temperatures. For a constant airflow, if the air-to-fuel ratio is adjusted from a very lean conditiontoward stoichiometric (balance air-to-fuel ratio for combustion), theexhaust gas temperature increases.

FIG. 5 shows exhaust gas temperature at idle as a function ofair-to-fuel ratio for a 6 cylinder engine under baseline (six cylindersfiring) and CDA operation. FIG. 5 shows CDA operation for threecylinders firing (which may be referred to herein as “3CF”), but thenumber of cylinders firing is not limited to three, and is instead anadditional variable that can be used to adjust the air-to-fuel ratio.Note that there are two basic regions of operation, a first region wherethe exhaust temperature variation with air-to-fuel ratio has a veryshallow slope, and small temperature gains are realized for largeair-to-fuel ratio changes (in the range of about 150:1 to about 40:1air-to-fuel ratio) and a second region where the exhaust temperaturevariation with air-to-fuel ratio has a very steep slope. FIG. 5 alsoshows that under idle conditions, air-to-fuel ratios greater than about35 are below the threshold for efficient SCR operation.

Under baseline operation a given, typical engine may idle with anair-to-fuel ratio around 60:1. Under 3CF CDA, the same engine may idlewith an air-to-fuel ratio around 40:1 and there is a slight increase inexhaust temperature realized for using CDA. A temperature rise of about20° C. is typical for a heavy-duty diesel engine at idle, which can beseen on the graph by comparing the exhaust temperature at an air-to-fuelratio of 60:1 to the exhaust temperature at an air-to-fuel ratio of40:1. If an electrical generator is driven by the engine and used to addheat to the exhaust by driving an electrical heater in the exhaust, thenthe mechanical load of the generator will cause the air-to-fuel ratio tobe reduced. This effect happens under both baseline and CDA operation.However, under baseline operation, loads in excess of practical limitswould need to be applied to achieve an air-to-fuel ratio in the regionof high exhaust temperature variation with air-to-fuel ratio.

Under CDA operation, in contrast, the starting air-to-fuel ratio is muchcloser to the “knee” of the air-to-fuel ratio curve where substantialincreases in exhaust temperature are realized for small changes in theair-to-fuel ratio. Loading the engine with an electric generator underCDA therefore results in a reduced air-to-fuel ratio in the range wheresubstantial increases in exhaust temperatures can be realized. Analyseswere performed to estimate the shift in air-to-fuel ratio realized by anidling engine under baseline and 3CF CDA operation by applying about 5kw of electric generation load on the engine. It was found that, forbaseline operation, the air-to-fuel ratio might be expected to shiftfrom about 60:1 to about 45:1 and the increase in exhaust temperaturemight be expected to be about 20° C. For 3CF operation of the sameengine, the result of the electric loading might be expected to shiftthe air-to-fuel ratio from about 40:1 to about 25:1 and the increase inthe exhaust gas temperature might be expected to be about 80° C., whichplaces the engine exhaust in a temperature range where high SCRefficiency may be realized.

The electric load applied to the engine and the number of cylindersfiring or deactivated may be manipulated to control the air-to-fuelratio in a range where manipulation of the air-to-fuel ratio results inrelatively high changes in exhaust temperature. Thus, the engine exhausttemperature may be maintained in an elevated state and high enough toensure sufficient SCR performance and efficiency to meet NOX emissionsstandards. Practical limits to electric generators, heaters, and wiringmay render such methods impractical for baseline (6 cylinder) operation.

A baseline energy equation that can be used to characterize the methodsand techniques described herein is Q₀={dot over (m)}×c_(p)×T, where Q₀is energy, m is the mass flow of exhaust, c_(p) is the specific heat ofthe exhaust, and T is the exhaust temperature. FIG. 6A provides aschematic diagram of a system including an engine and an EAS where thisequation applies. In this equation, the energy of the exhaust from theengine is a function of the mass flow and temperature of the exhaust.Another energy equation can be formulated that governs the same systembut with the addition of supplemental energy, such as electrical energy,into the exhaust to raise the temperature of the exhaust, as follows:

$T_{2} = {T_{1} + {\frac{Q_{E}}{\overset{.}{m}{xcp}}.}}$

FIG. 6B provides a schematic diagram of a system including an engine andan EAS where this equation applies.

Another equation can be formulated that governs the system of FIG. 6Abut with reduced air flow in the engine using 3CF CDA to increase theexhaust temperature at a given engine speed due to a reduced air-to-fuelratio and reduced pumping losses from the engine (due to fewer firingcylinders), as follows:

$Q_{0} = {\frac{\overset{.}{m}}{2}{xc}_{p}{{xT}_{3}.}}$

FIG. 6C provides a schematic diagram of a system including an engine andan EAS where this equation applies. Another equation can be formulatedthat governs the system of FIG. 6A but with both reduced air flow in theengine using 3CF CDA, a load applied to the engine in the form of anelectrical generator, and addition of supplemental energy, such aselectrical energy from the electrical generator, into the exhaust toraise the temperature of the exhaust as follows:

$T_{5} = {T_{4} + {\frac{Q_{E}}{\frac{\overset{.}{m}}{2}{xcp}}.}}$

FIG. 6D provides a schematic diagram of a system including an engine andan EAS where this equation applies.

FIG. 7 illustrates a schematic diagram of a vehicle 100, which may be aheavy-duty vehicle, with an internal combustion engine 102, which may bea diesel engine, an exhaust after-treatment system 104, a set of atleast four wheels 106 configured to be powered and driven by the engine102, an electrical generator 108, and a control system 110, which canperform the methods described herein. When the vehicle 100 is inoperation, the control system 110 can be used to control operation ofportions of the vehicle 100, including its internal combustion engine102 and its exhaust after-treatment system 104. For example, the controlsystem 110 may be configured to control the engine 102 to idle with anynumber of its cylinders firing and any number of its cylindersdeactivated, to control the engine 102 to drive the electric generator108, and to direct electrical energy generated by the electricalgenerator 108 into an exhaust gas stream at a location between theengine 102 and the exhaust after-treatment system 104. As anotherexample, the control system 110 may be configured to control the exhaustafter-treatment system 104 and components thereof, including a dieseloxidation catalyst (DOC) to oxidize unburned fuel and carbon monoxide, adiesel particulate filter (DPF) to control particulate matter (PM), aselective catalytic reduction (SCR) system to reduce oxides of nitrogen(NOX), and an ammonia oxidation catalyst (AMOX) system.

In some embodiments, the vehicle 100 may include a plurality of sensorsthat collect and transmit data regarding operating parameters of thevehicle 100 to the control system 110, such as continuously. Forexample, such sensors may collect and transmit data regarding an exhaustgas temperature and/or an operating speed of the internal combustionengine 102 (e.g., in RPM) to the control system 110. In someembodiments, the control system 110 may control operation of the vehicle100, such as in accordance with any of the techniques described herein,based on such measurements and data, such as when such measurements fallbelow certain specified thresholds, e.g., when the exhaust gastemperature falls below any of the exhaust gas temperatures mentionedherein, such as 190° C., or when the internal combustion engine 102 isidling, as identified, for example, when the operating speed of theinternal combustion engine 102 falls below 550 RPM, or 600 RPM, or 650RPM, or 700 RPM, or 750 RPM, or 800 RPM.

The methods described herein use the compounding effect of reducedexhaust flow, manipulation of the air-to-fuel ratio using mechanicalloading by a generator or alternator, and input of electrical power intothe exhaust as supplemental heat to obtain a large increase in idlingand low load exhaust gas temperature from an engine. An additionalfeature of such embodiments is that they provide higher exhaust gastemperature at lower fuel consumption compared to baseline idlestrategies.

Analyses were performed to determine the effect of the systems, methods,and techniques described herein on overall fuel efficiency of heavy dutyvehicles over the proposed LLC. Results were variable, but it wasgenerally found that heating exhaust gas flows to temperatures suitablefor effective SCR performance by CDA and electric heating, as describedherein, resulted in a fuel savings relative to baseline operatingconditions in which the exhaust is not heated, as well as with respectto electric heating techniques alone. U.S. provisional patentapplication No. 62/868,689, filed Jun. 28, 2019, is hereby incorporatedherein by reference in its entirety. The various embodiments describedabove can be combined to provide further embodiments. These and otherchanges can be made to the embodiments in light of the above-detaileddescription. In general, in the following claims, the terms used shouldnot be construed to limit the claims to the specific embodimentsdisclosed in the specification and the claims, but should be construedto include all possible embodiments along with the full scope ofequivalents to which such claims are entitled. Accordingly, the claimsare not limited by the disclosure.

1. A method, comprising: warm idling an internal combustion engine,thereby producing exhaust; reducing a volumetric flow rate of airthrough the engine; increasing a mechanical load to the engine, therebyincreasing an amount of fuel demanded by the engine; and inputtingenergy from a source of electrical energy into the exhaust.
 2. Themethod of claim 1, wherein increasing a mechanical load to the engineincludes using the running engine to drive an electric generator.
 3. Themethod of claim 2, further comprising charging a battery with electricenergy generated by the electric generator.
 4. The method of claim 2wherein the electric generator is the source of electric energy.
 5. Themethod of claim 1 wherein inputting energy into the exhaust includesusing an electrically heated catalyst system.
 6. The method of claim 1wherein reducing the volumetric flow rate of air through the engineincludes reducing the volumetric flow rate of air through the engine byhalf.
 7. The method of claim 1 wherein reducing the volumetric flow rateof air through the engine includes deactivating one or more cylinders ofthe engine.
 8. The method of claim 1 wherein reducing the volumetricflow rate of air through the engine includes recirculating the exhaustthrough the engine.
 9. The method of claim 1 wherein reducing thevolumetric flow rate of air through the engine includes reducing an idlespeed of the engine.
 10. The method of claim 1 wherein reducing avolumetric flow rate of air through the engine is performedsimultaneously with increasing a mechanical load to the engine andinputting energy into the exhaust.
 11. The method of claim 1 whereinreducing a volumetric flow rate of air through the engine is performedconcurrently with increasing a mechanical load to the engine andinputting energy into the exhaust.
 12. A method, comprising,simultaneously: idling an internal combustion engine with at least onecylinder of the engine firing and at least one cylinder of the enginedeactivated, thereby producing exhaust; using the idling engine to drivean electric generator; and inputting electrical energy generated by theelectric generator into the exhaust.
 13. The method of claim 12 wherein:idling the internal combustion engine with at least one cylinder of theengine deactivated reduces a volumetric flow rate of air through theengine relative to idling the engine with all cylinders of the enginefiring; using the idling engine to drive an electric generator applies amechanical load to the engine and increases an amount of fuel demandedby the engine relative to idling the engine without using the idlingengine to drive an electric generator; reducing the volumetric flow rateof air through the engine and increasing the amount of fuel demanded bythe engine reduces an air-to-fuel ratio within the engine and increasesa temperature of the exhaust; and inputting electrical energy generatedby the electric generator into the exhaust increases the temperature ofthe exhaust.
 14. A heavy duty vehicle, comprising: an internalcombustion engine; an exhaust after-treatment system; and a controlsystem; wherein the control system, in operation, controls the vehicle,the internal combustion engine, and the exhaust after-treatment systemto simultaneously: idle the internal combustion engine with at least onecylinder of the engine firing and at least one cylinder of the enginedeactivated; use the internal combustion engine to drive an electricgenerator; and input electrical energy generated by the electricgenerator into exhaust produced by the internal combustion engine. 15.The vehicle of claim 14 wherein the control system, in operation,controls the vehicle, the internal combustion engine, and the exhaustafter-treatment system to simultaneously: warm idle the internalcombustion engine with at least one cylinder of the engine firing and atleast one cylinder of the engine deactivated; use the internalcombustion engine to drive the electric generator; and input theelectrical energy generated by the electric generator into exhaustproduced by the internal combustion engine.
 16. The vehicle of claim 14wherein the internal combustion engine is a diesel engine.
 17. Thevehicle of claim 14 wherein the exhaust after-treatment system includesa diesel oxidation catalyst.
 18. The vehicle of claim 14 wherein theexhaust after-treatment system includes a diesel particulate filter. 19.The vehicle of claim 14 wherein the exhaust after-treatment systemincludes a selective catalytic reduction system.
 20. The vehicle ofclaim 14 wherein the exhaust after-treatment system includes an ammoniaoxidation catalyst system.